The present invention relates to variable valve actuating mechanisms.
Modern internal combustion engines may incorporate advanced throttle control systems, such as, for example, intake valve throttle control systems, to improve fuel economy and performance. Generally, intake valve throttle control systems control the flow of gas and air into and out of the engine cylinders by varying the timing, duration and/or lift (i.e., the valve lift profile) of the cylinder valves in response to engine operating parameters, such as engine load, speed, and driver input. For example, the valve lift profile is varied from a relatively high-lift profile under high-load engine operating conditions to a reduced/lower lift profile under engine operating conditions of moderate and low loads.
Intake valve throttle control systems vary the valve lift profile through the use of variously-configured mechanical and/or electromechanical devices, collectively referred to herein as variable valve actuation (VVA) mechanisms. Several examples of particular embodiments of VVA mechanisms are detailed in commonly-assigned U.S. Pat. No. 5,937,809, the disclosure of which is incorporated herein by reference.
Generally, a conventional VVA mechanism includes a rocker arm that is displaced in a generally radial direction by a corresponding input cam of an input shaft, such as the engine camshaft. The displacement of the rocker arm is transferred via a link arm to pivotal oscillation of an output cam relative to the input shaft. The pivotal oscillation of the output cam is transferred to actuation of an associated valve by a cam follower, such as, for example, a roller finger follower. A desired valve lift profile is obtained by orienting the output cam into a starting or base angular orientation relative to the cam follower and/or the central axis of the input shaft. The starting or base angular orientation of the output cam determines the portion of the lift profile thereof that engages the cam follower as the output cam is pivotally oscillated, and thereby determines the valve lift profile. The starting or base angular orientation of the output cam is set via a control shaft that pivots a frame member and, via the rocker and link, the output cam relative to the cam follower and/or the central axis of the input shaft.
In a multi-cylinder engine, the camshaft extends the entire length of the engine cylinder head and includes at least one cam lobe for each cylinder. The cam lobes are typically formed integrally with the camshaft, such as by machining, and are spaced along the length of the camshaft. At least a portion of the cam lobes extend outside the diameter of the camshaft. Thus, the components of the WA that are slidingly received over and mounted onto the camshaft can not be slid past the point where the first cam lobe is positioned on the camshaft. Several approaches exist that enable placement of the components of a VVA along the length of a camshaft, and on either side of the cam lobes formed thereon, thereby enabling a VVA mechanism to be associated with each cylinder.
One approach segments the camshaft into multiple sections, each of which correspond to a respective cylinder of the engine. Segmentation of the camshaft permits components of the VVA mechanism to be slid into position on either side of the cam lobe. Further, segmentation of the camshaft enables VVA mechanisms to be installed for each cylinder. However, segmentation of the camshaft increases the number of machining operations required and thus increases machining costs. Further, using segmented camshafts for each cylinder requires precise alignment of the segments relative to each other. The alignment process is time-consuming, labor intensive and costly.
Another approach uses oversized WA components. The components of the VVA mechanism are made larger so that they can be slid over the cam lobes and into association with each cylinder. However, oversized components are more costly to produce, consume more space within the engine cylinder head, and undesirably increase the weight of an engine and/or vehicle.
Yet another approach is to split the components of the VVA that are pivotally coupled to the input or camshaft into two pieces. For example, an output cam is split into upper and lower pieces. The pieces are then placed in the desired position on the camshaft and coupled together with fasteners, such as bolts, thereby pivotally coupling the split output cam to the camshaft. However, the fasteners increase the part count and make assembly of the VVA mechanism more time consuming and more complex. Further, fasteners may become loose over time or even disengage, causing the VVA mechanism to malfunction and potentially causing damage to the engine.
Therefore, what is needed in the art is a variable valve mechanism having a one-piece, unitary camshaft, thereby eliminating the need to align camshaft segments with each other.
Furthermore, what is needed in the art is a WA mechanism having fewer component parts.
Still further, what is needed in the art is a WA mechanism that does not require the use of over-sized component parts in order to be positioned on either side of a cam lobe and/or at any position along the camshaft.
Moreover, what is needed in the art is a VVA mechanism that does not require the use of split components in order to be positioned on either side of a cam lobe and/or at any position along the camshaft.
The present invention provides a variable valve actuation mechanism having an output cam and frame assembly that engage and are retained upon the camshaft of an engine with a snap fit.
The invention comprises, in one form thereof, a partial wrap output cam assembly and a partial wrap frame assembly. Each of the partial wrap cam assembly and the partial wrap frame assembly include a respective body and a respective shaft engaging means coupled to the body. The shaft-engaging means are configured for engaging an input shaft with a snap fit to thereby pivotally dispose the output cam assembly and the frame assembly upon the input shaft.
An advantage of the present invention is that the partial wrap frame and output cam assemblies eliminate the need to segment the camshaft, and the alignment process associated with a segmented camshaft.
A further advantage of the present invention is that the components can be placed on either side of an input cam lobe, or virtually anywhere along the length of a camshaft or input shaft.
An even further advantage of the present invention is that the VVA mechanism of the present invention can be at least partially assembled and retained upon a camshaft, thereby facilitating final installation in an engine.